1. Field of the Invention
The present invention relates to methods and apparatus for administration of drugs. More particularly, the present invention relates to using controlled heat and other physical means to improve dermal, mucosal, and injection administration of drugs.
2. State of the Art
The dermal administration of pharmaceutically active compounds involves the direct application of a pharmaceutically active formulation(s) to the skin, wherein the skin absorbs a portion of the pharmaceutically active compound which is then taken up by the blood stream. Such administration has long been known in the practice of medicine and continues to be an important technique in the delivery of pharmaceutically active compounds. For example, U.S. Pat. No. 4,286,592 issued Sep. 1, 1981 to Chandrasekaran shows a bandage for administering drugs to a user""s skin consisting of an impermeable backing layer, a drug reservoir layer composed of a drug and a carrier, and a contact adhesive layer by which the bandage is affixed to the skin.
Such dermal administration offers many important advantages over other delivery techniques, such as injection, oral tablets and capsules. These advantages include being noninvasive (thus, less risk of infection), avoiding first pass metabolism (metabolism of the drug in the liver when the drug is taken orally and absorbed through the gastrointestinal tract), and avoiding of high peaks and low valleys of concentration of pharmaceutically active compounds in a patient""s bloodstream. In particular, high peaks and low valleys of concentration are typical in injection and oral administrations and are often associated with undesirable side effects and/or less than satisfactory intended effects.
The term xe2x80x9cdermal drug delivery systemxe2x80x9d or xe2x80x9cDDDSxe2x80x9d, as used herein, is defined as an article or apparatus containing pharmaceutically active compound(s) for delivery into the skin, the regional tissues under the skin, the systemic circulation, or other targeting site(s) in a human body via skin permeation. The term xe2x80x9cDDDSxe2x80x9d in this application, unless otherwise specified, only refer to those systems in which the main driving force for drug permeation is the drug concentration gradient.
The term xe2x80x9cskinxe2x80x9d, as used herein, is defined to include stratum comeum covered skin and mucosal membranes.
The term xe2x80x9cdrugxe2x80x9d, as used herein, is defined to include any pharmaceutically active compound including but not limited to compounds that treat diseases, injuries, undesirable symptoms, and improve or maintain health.
The terms xe2x80x9ctargeted areaxe2x80x9d or xe2x80x9ctargeted areasxe2x80x9d, as used herein, are defined to include a systemic bloodstream of a human body, areas of a human body which can be reached by a systemic bloodstream including, but not limited to muscles, brain, liver, kidneys, etc., and body tissue regions proximate a location of an administered drug.
In DDDSs, a drug(s) is usually contained in a formulation, such as a hydro-alcohol gel, and may include a rate limiting membrane between the formulation and skin for minimizing the variation in the permeation of the drug. When a DDDS is applied to skin, the drug begins to transport out of the formulation, and transport across the rate limiting membrane (if present). The drug then enters the skin, enters blood vessels and tissues under the skin, and is taken into the systemic circulation of the body by the blood. At least some DDDSs have certain amount of pharmaceutically active compound in or on the skin side of the rate limiting membrane (if present) prior to use. In those DDDSs, that portion of the drug on the skin side of the rate limiting membrane will enter the skin without passing through the rate limiting membrane. For many drugs, a significant portion of the dermally absorbed drug is stored in the skin and/or tissues under the skin (hereinafter referred as xe2x80x9cdepot sitesxe2x80x9d) before being gradually taken into the systemic circulation (hereinafter referred as xe2x80x9cdepot effectxe2x80x9d). This depot effect is believed to be at least partially responsible for the delayed appearance of the drug in the systemic circulation after the application of some DDDSs and for continued delivery of the drug into the systemic circulation after the removal of some DDDSs from the skin.
After placing a DDDS on the skin, the drug concentration in the blood typically remains at or near zero for a period of time, before starting to gradually increase and reach a concentration deemed to be medicinally beneficial, called the xe2x80x9ctherapeutic levelxe2x80x9d (the time it takes to reach the therapeutic level is referred to hereinafter as the xe2x80x9conset timexe2x80x9d). Ideally, the concentration of the drug in the bloodstream should plateau (i.e., reach a substantially steady state) at a level slightly higher than the therapeutic level and should remain there for extended period of time. For a given person and a given DDDS, the xe2x80x9cconcentration of the drug in the bloodstream vs. timexe2x80x9d relationship usually cannot be altered under normal application conditions.
The onset time and the delivery rate of the drug into the targeted area(s) of the body for a typical DDDS are usually determined by several factors, including: the rate of release of the drug from the formulation, the permeability of the drug across the rate limiting membrane (if a rate limiting membrane is utilized), the permeability of the drug across the skin (especially the stratum comeum layer), drug storage in and release from the depot sites, the permeability of the walls of the blood vessels, and the circulation of blood and other body fluid in the tissues (including the skin) under and around the DDDS. Although these primary factors affecting onset time and delivery rate are known, no existing DDDS is designed to have alterable delivery rate in the course of the application of the drug.
While a DDDS works well in many aspects, current dermal drug delivery technology has some serious limitations, including: 1) the onset time being undesirably long for many DDDSs; 2) the rate that the drug is taken into the systemic circulation or the targeted area(s) of the body cannot be easily varied once the DDDS is applied onto the skin and, when the steady state delivery rate is achieved, it cannot be easily changed; and 3) the skin permeability being so low that many drugs are excluded from dermal delivery because the amount of drug delivered is not high enough to reach a therapeutic level. In addition, temperature variations in the skin and the DDDS are believed contribute to the variation of dermal absorption of drugs.
It is known that elevated temperature can increase the absorption of drugs through the skin. U.S. Pat. No. 4,898,592, issued Feb. 6, 1990 to Latzke et al., relates to a device for the application of heated transdermally absorbable active substances which includes a carrier impregnated with a transdermally absorbable active substance and a support. The support is a laminate made up of one or more polymeric layers and optionally includes a heat conductive element. This heat conductive element is used for distribution of the patient""s body heat such that absorption of the active substance is enhanced. U.S. Pat. No. 4,230,105, issued Oct. 28, 1980 to Harwood, discloses a bandage with a drug and a heat-generating substance, preferably intermixed, to enhance the rate of absorption of the drug by a user""s skin. Separate drug and heat-generating substance layers are also disclosed. U.S. Pat. No. 4,685,911, issued Aug. 11, 1987 to Konno et al., discloses a skin patch including a drug component, and an optional heating element for melting the drug-containing formulation if body temperature is inadequate to do so.
Another area of administration involves delivering drugs in controlled/extended release form/formulations (xe2x80x9cform/formulationxe2x80x9d) into the skin or tissues under the skin (the residing place for these form/formulations are hereinafter referred as xe2x80x9cstorage sitesxe2x80x9d) which results in the drugs being released from the storage sites in a controlled/extended fashion. The most common technique to deliver the form/formulations into the storage sites is by injection. Other techniques may also be used, such as implantation and forcing the form/formulation into the skin with high-speed hitting. However, once the form/formulation is delivered into the storage sites, it is usually difficult to alter the rate, known as the xe2x80x9crelease ratexe2x80x9d, that the drug is released from the form/formulation at the storage sites, and taken into the systemic circulation or the targeted area(s) of the body.
Yet another area of administration involves injecting drugs subcutaneously or intramuscularly. In some clinical situations, it is beneficial to accelerate the speed of drug absorption into the systemic circulation or other targeted areas(s) in the body after such injection.
Therefore, it would be advantageous to develop methods and apparatus to improve the drug administration of DDDSs, and, more specifically, to make the use of DDDSs more flexible, controllable, and titratable (varying the drug delivery rate, amount, or period according to the biological effect of the drug) to better accommodate various clinical needs. It would also be advantageous to develop methods and apparatus to make dermal delivery possible for drugs which are currently excluded because of low skin permeability. It would further be advantageous to develop means to alter mainly to increase the drug absorption rate from the storage sites or injection sites in such ways that can accommodate certain clinical needs.
The present invention relates to various methods and apparatus for improved dermal and mucosal administration of drugs through the use of controlled heat and other physical means. The present invention further relates to methods and apparatus for using controlled heat and other physical means to alter, mainly increase, the drug release rate from the storage sites or injection sites in such ways to accommodate certain clinical needs.
In the application of a DDDS, the absorption of the drug is usually determined by a number of factors including: the diffusion coefficient of drug molecules in the drug formulation, the permeability coefficient of the drug across the rate limiting membrane (if one is used in the DDDS), the concentration of dissolved drug in the formulation, the skin permeability of the drug, drug storage in and release from the depot sites, the body fluid (including blood) circulation in the skin and/or other tissues under the skin, and permeability of the walls of capillary blood vessels in the sub-skin tissues. Thus, in order to address the limitations of the current dermal drug delivery technologies, it is desirable to have control over and have the capability to alter these drug absorption factors. It is believed that controlled heating/cooling can potentially affect each one of the above factors.
Specifically, increased temperature generally can increase diffusion coefficients of the drugs in the formulations and their permeability across the rate limiting membrane and skin. Increased heat also increases the blood and/or other body fluid flow in the tissues under the DDDS, which should carry the drug molecules into the systemic circulation at faster rates. Additionally, increased temperature also increases the permeability of the walls of the capillary blood vessels in the sub-skin tissues. Furthermore, increased temperature can increase the solubility of most, if not all, drugs in their formulations which, in formulations with undissolved drugs, should increase permeation driving force. Of course, cooling should have substantially the opposite effect. Thus, the present invention uses controlled heating/cooling to affect each of the above factors for obtaining controllable dermal absorption of drugs.
The present invention also uses controlled heating/cooling in several novel ways to make dermal drug delivery more flexible and more controllable in order to deal with various clinical conditions and to meet the needs of individual patients. More broadly, this invention provides novel methods and apparatus for controlled heating/cooling (hereinafter xe2x80x9ctemperature control apparatusxe2x80x9d) during the application of the DDDS, such that heating can be initiated, reduced, increased, and stopped to accommodate the needs.
Another embodiment of the present invention is to determine the duration of controlled heating on DDDS based on the effect of the drug for obtaining adequate amount of the extra drug and minimizing under-treatment and side effects associated with under and over dosing.
Through the proper selection, based on the specific application and/or the individual patient""s need, of the moment(s) to initiate controlled heating, heating temperature, and moment(s) to stop the controlled heating, the following control/manipulation of the absorption rates should be achieved: 1) shorten the onset time of the drug in the DDDS without significantly changing its steady state delivery rates; 2) provide proper amount of extra drug during the application of a DDDS when needed; and 3) increase the drug absorption rate throughout a significant period of duration or throughout the entire duration of the DDDS application.
Shortening of onset time is important in situations where the DDDS provides adequate steady state deliver rates, but the onset is too slow. Providing the proper amount of extra drug is important where a DDDS delivers adequate xe2x80x9cbaselinexe2x80x9d amount of the drug, but the patient needs extra drug at particular moment(s) for particular period(s) of time during the application of the DDDS. Increasing the drug absorption rate is used for the patients who need higher drug delivery rates from the DDDS.
The first of above approach can be achieved by applying controlled heating at the starting time of the DDDS application, and design the heating to last long enough to cause the concentration of the drug in the systemic circulation or other targeted area of the body to rise toward the therapeutic levels, and stops (may be gradually) shortly after that. The second approach may be achieved by applying controlled heat when a need to obtain extra drug are rises, and terminating the controlled heating either at a predetermined moment or when the desired effect of the extra drug is achieved. The third approach can be achieved by applying the controlled heat at the starting time of the DDDS application. In all those three approaches, temperature of the controlled heating needs to be designed to control the degree of increase in said that drug delivery rates.
Such embodiments are particularly useful in situations where the user of a DDDS gets adequate drug absorption most of the time, but there are periods of time in which increased or decreased drug absorption is desirable. For example, during the treatment of cancer patients with an analgesic, such as with Duragesic(copyright) dermal fentanyl patches (distributed by Janssen Pharmaceutica, Inc. of Piscataway, N.J., USA), xe2x80x9cbreakthroughxe2x80x9d pain (a suddenly increased and relatively short lasting pain, in addition to a continuous xe2x80x9cbaselinexe2x80x9d pain) may occur. An additional analgesic dose, in the form of a tablet, an oral or nasal mucosal absorption dosage form, or an injection needs to be given to treat the breakthrough pain. But with the help of controlled heat, one single DDDS may take care of both baseline pain and episodes of breakthrough pain. With the help of controlled heat, a heating patch can be placed on top of the Duragesic(copyright) patch when an episode of breakthrough pain occurs to deliver more fentanyl into the systemic circulation. The heating duration of the heating patch is preferably designed to be long enough to deliver sufficient extra fentanyl, but not long enough to deliver the extra amount of fentanyl that may pose a risk to the patient. The patient may also remove the heating patch when the breakthrough pain begins to diminish. Thus, with the help of controlled heat, one single Duragesic(copyright) dermal fentanyl patch may take care of both baseline pain and episodes of breakthrough pain. For another example, a dermal nicotine patch user may obtain extra nicotine for a suddenly increased nicotine craving by heating the nicotine patch.
Due to low skin permeability of the skin, onset times of conventional DDDSs are usually quite long, and often undesirably long. Thus, another aspect of the present invention is to provide methods and apparatus for using controlled heat to shorten the onset times of DDDSs, preferably without substantially changing the steady state drug delivery rates. A particularly useful application of this aspect of the present invention is to provide a controlled heating apparatus for use with conventional, commercially available DDDSs to shorten the onset times in clinical use, without having to re-design the DDDSs or adjust their steady state drug delivery rates.
It is believed that an important cause for variation in drug absorption in DDDSs is variation in temperature of the DDDSs and the adjacent skin caused by variations in ambient temperature and/or physical condition of the person. This temperature variation can, of course, potentially affect all of the factors that collectively determine the ultimate drug delivery rates of the DDDSs. Thus, the present invention of providing methods and apparatus to use controlled heating/cooling also minimizes the variation in temperature of the skin and the DDDSs applied on the skin. It is also contemplated that an insulating material can be incorporated with the controlled temperature apparatus to assist in not only minimizing the temperature variation, but also increasing the temperature of the DDDS and the skin under it (by decreasing heat loss), each of which tend to increase dermal drug absorption.
The present invention also relates to methods and apparatus for using an insulating device, such as a cover made of insulating material (such as closed-cell foam tape) with adhesive edges, and a size slightly larger than the DDDS or the area over an injected drug, to cover the DDDS/injected drug when the DDDS and/or the skin of the user is exposed to extreme temperature (such as a hot shower or bath, direct sunlight, etc.).
An important area in modem anesthesiology is patient controlled analgesia (hereinafter xe2x80x9cPCAxe2x80x9d), in which the patient gives himself a dose of analgesic when he feels the need. The ranges of the dose and dosing frequency are usually set by a care giver (i.e., caring physician, nurse, etc.). In many PCA situations, the patient receives a baseline rate of analgesic, and gets extra bolus analgesic when he feels that it is needed. The technology in the present invention may be used for a PCA in which the patient gets the baseline dose by a regular dermal analgesic patch and the extra (xe2x80x9crescuexe2x80x9d) dose by heating the dermal analgesic patch. The heating temperature and duration needs to be designed to deliver a proper amount of extra dose.
Drugs in controlled or extended release forms or formulations may be delivered into depot/storage sites in the skin and/or the tissues under the skin with methods such as injection, implantation, hitting the drug/drug formulation on the skin with supersonic speed, and embedding the drug/drug formulation onto the skin. The controlled/extended form/formulation allows the drug to be released gradually into the surrounding tissues and/or systemic circulation over an extended period of time. For instance, extended release insulin (such as Ultralente(copyright) zinc insulinxe2x80x94Eli Lilly and Co.) can be injected subcutaneously to deliver insulin into the patient""s systemic circulation over an extended period of time. However, once the drug in the controlled/extended form/formulation is delivered to the storage sites, it is usually difficult to alter or control the course of drug release. The apparatus and methods of the present invention allow controlled heat to increase and controlled cooling to decrease, the drug release from the controlled/extended form/formulation after it is delivered into the depot/storage sites. For example, many diabetic patients need additional insulin shortly before meals to suppress the blood sugar increase resulting from the meals. However, the release rate of the subcutaneously injected extended release insulin is relatively constant. With the methods and apparatus in the invention, a diabetic patient may inject a subcutaneous extended release insulin in the morning and apply controlled heat on the skin of the injection site for a duration of time shortly before ingestion of a meal to obtain additional insulin to suppress the sugar from the meal. The controlled heat increases the flow of blood and other body fluid surrounding the storage sites and is believed to increase the dissolution rate of insulin. It is, of course, understood that whether a given controlled/extended release formulation in the depot/storage sites can actually release extra drug with increased temperature depends on the nature of the drug form/formulation. However, since heat is known or expected to increase the diffusion speed of drugs in their formulations, increase the permeability of blood vessel walls, and increases the circulation of body fluid surrounding the depot sites, each of which tend to favor increased drug release, the heat-induced extra drug release is expected to take place for many, if not most, controlled/extended drug form/formulation delivered into sub-skin storage sites.
One important aspect of the present invention is to properly choose the temperature of the controlled heat and the moment(s) to initiate and stop the controlled heat in the applications with injected drug formulations, especially extended/controlled release formulations, to accommodate the needs of different therapies and individual patients, in ways similar to the applications with DDDSs discussed above.
Many biodegradable polymers may be used to make controlled/extended release formulations. Of particular note are the biogradable lactic/glycolic acid polymers described in Chapters 29 and 33 of Encyclopedic Handbook of Biomaterials and Bioengineering, edited by Donald L. Wise, et al., publ. Marcel Dekker, 1995, hereby incorporated herein by reference. It is one important aspect of the present invention to use controlled heat, as discussed above, to control/regulate drug release rates from controlled/extended release formulations made with such polymers, and preferably, prepared using the methods described in the Encyclopedic Handbook of Biomaterials and Bioengineering. 
For drugs where quick systemic absorption is important, the present invention may be beneficial. For example, it is generally agreed that to successfully treat a migraine headache, concentrations of an anti-migraine drug, such as dihydroergotamine, in the bloodstream must reach a therapeutic level within a certain time from the onset of migraine headache. In such situations, the heating devices, as discussed above, may be used with normal injection of drugs. Since heat can usually increase the diffusion speed of drugs in their formulations, increase the permeability of blood vessel walls, and increases the circulation of body fluid surrounding the injection site, the drug will enter the system circulation more quickly.
One of the more important aspects of the present invention is the apparatus for generating and providing controlled heating. These controlled heat generating apparatus generally comprise a heat generating portion and a means to pass the heat generated by the heat generating portion to the DDDSs, the skin, and/or the sub-skin depot and storage sites. These controlled heat generating apparatus generally further include a mechanism (such as tape, adhesive, and the like) for affixing apparatus onto the DDDSs and/or the skin. Preferably, the affixation mechanism securely holds the controlled heat generating apparatus in place while in use, but it also allows relatively easy removal after use. Additionally, these controlled heat generating apparatus may further include a mechanism for terminating the generation of heat. The shape and size of the bottom of the controlled heat generating apparatus are generally specially made to accommodate the DDDSs with which they are to be employed.
One embodiment of a controlled heat generating apparatus is a shallow chamber including non-air permeable side wall(s), a bottom wall, and a non-air permeable top wall which has area(s) with limited and desired air permeability (e.g., holes covered with a microporous membrane). A heat generating medium is disposed within the shallow chamber. The heat generating medium preferably comprises a mixture of iron powder, activated carbon, salt, water, and, optionally, sawdust. The controlled heat generating apparatus is preferably stored in an air-tight container from which it is removed prior to use. After removal from the air-tight container, oxygen in the atmosphere (xe2x80x9cambient oxygenxe2x80x9d) flows into heat generating medium through the areas on the non-air permeable top with desired air-permeability to initiate a heat generating oxidation reaction (i.e., an exothermic reaction). The desired heating temperature and duration can be obtained by selecting the air exposure of the top (e.g., selecting the right size and number of holes on the cover and/or selecting the microporous membrane covering the holes for a specific air permeability), and/or by selecting the right quantities and/or ratios of components of the heat generating medium.
This embodiment of the controlled heat generating apparatus preferably includes a mechanism for affixing the controlled heat generating apparatus onto the skin or a DDDS that is applied to the skin. For applications where the removal or termination of the heating might be necessary, the heat generating apparatus may also have a mechanism for allowing easy removal from the DDDS and/or the skin or for termination of the heating. One mechanism for allowing easy removal of the shallow chamber from a DDDS without removing the latter from the skin comprises a layer of adhesive on the side walls of the heat generating apparatus with an non-adhesive area or less adhesive area (less adhesive than the adhesive affixing the DDDS to the skin) at the bottom of the shallow chamber, with the non- or less adhesive area having a shape similar to that of the DDDS. When such a heat generating apparatus is applied onto the DDDS which is on the skin, the adhesive at the bottom of the side walls of the heat generating apparatus adheres to the skin, and non- or less adhesive part is on top of, but not adhered or not strongly adhered to, the DDDS. This allows for removal of the heat generating apparatus without disturbing the DDDS.
Although one application of such a heat generating apparatus is to be used in conjunction with a DDDS, it is understood that the heat generating apparatus can also be applied directly to the skin to increase the release of drugs from depot sites or sites of injection or implantation of controlled released drugs (storage sites), or to accelerate the absorption of subcutaneously or intramuscularly injected drugs.
The heat generating mechanism of the present invention for the controlled heat generating apparatus is not limited to the preferred exothermic reaction mixture of iron powder, activated carbon, salt, water, and, optionally, sawdust, but may include a heating unit whose heat is generated by electricity. The electric heating unit, preferably, includes a two dimensional surface to pass the heat to the DDDS and/or the skin. The electric heating unit may also include a temperature feedback system and a temperature sensor that can be placed on the DDDS or the skin. The temperature sensor monitors the temperature at the DDDS or skin and transmits an electric signal based on the sensed temperature to a controller which regulates the electric current or voltage to the electric heating unit to keep the temperature at the DDDS or skin at desired levels. Preferably, a double sided adhesive tape can be used to affix the electric heating unit onto the skin.
The heat generating mechanism may also comprise an infrared generating unit and a mechanism to direct the infrared radiation onto the DDDS or the skin. It may also have a temperature feedback system and a temperature sensor that can be placed on the DDDS or the skin to control the intensity of the infrared emission to maintain the temperature at the DDDS or skin at desired levels.
The heat generating mechanism may further comprise a microwave generation unit and a mechanism to direct the microwave radiation onto the DDDS or the skin. Again, the heat generating mechanism may have a temperature feedback system and a temperature sensor to regulate the intensity of the microwave emission to maintain the temperature at the DDDS or skin at desired levels.
The heat generating mechanism may yet further comprise a container containing supercooled liquid which generates heat from crystallization (xe2x80x9cexothermicxe2x80x9d). The crystallization is initiated within the container, such as by bending a metal piece in the supercooled liquid, and the container is placed on a DDDS or on the skin. The heat which is released from the crystallization process is passed to the DDDS and/or the skin. However, heat generated by crystallization usually does not maintain a constant level over extended time. Thus, such a heat generating mechanism is not ideal for applications where elevated temperature in a narrow range over an extended time is necessary, but is useful where only a short heating duration is needed, such as with a DDDS that would benefit from short heating duration to minimize the onset time.
Although, in general, most benefits for DDDSs are realized from increased drug absorption and release rates by heating, there are circumstances where it may be desirable to be able to both increase and decrease the drug absorption and release rates. It is understood that for a more complete control in dermal and controlled/extended release drug administration that a mechanism for providing both heating or cooling, depending on need, would be advantageous. Thus, a novel approach of this invention is to provide methods and apparatus for providing heating or cooling to the DDDSs, the skin and/or the tissues under it, or the controlled/extended release drug form/formulation in the skin or the tissues under the skin, such that the drug absorption and/or release can be controlled. The heating/cooling mechanism comprises a thermoelectric module which functions as a heat pump wherein the power supply may be reversed depending on whether heating or cooling is desired. A cooling mechanism can include an endothermic crystallization mechanism similar to the exothermic crystallization mechanism discussed above.
It is, of course, understood that the use of controlled heating and/or cooling to control drug absorption and/or release are equally applicable to controlled/extended form/formulations after they are delivered into the skin and/or tissues under the skin. However, physical mechanisms other than heating and/or cooling may also be used for the same purpose. Thus, it is novel approach of this invention to provide methods and apparatus to use ultrasound, electric current, and mechanical vibration to induce extra drug release from controlled/extended release form/formulations which are already delivered into the body and that are responsive to these physical induction means.